The present invention relates to a centrifuge for separating massecuite into solid and liquid fractions. More particularly, the present invention relates to a periodically operating centrifuge for separating massecuite, including a swingably suspended rotatable drum which has a flat bottom, a supporting sieve for fine-meshed sieve arranged on an inner surface of the drum and separating massecuite into its constituent liquid and solid fractions as well as forming an intermediate space for the separated liquid fractions or sirup, and holes formed in a circumferential wall in the regions of a top and bottom wall for discharging the centrifuged liquid fraction.
Intermittently operating centrifuges for separating massecuite of the above-mentioned known type have been proposed in the art. They serve for centrifuging of white sugar and have a rotatable shaft and a drum fixedly connected to the latter which are swingably suspended so as to compensate for imbalance during the operation.
For this purpose a centrifuge has been proposed (German Auslegeschrift No. 1208694) in which the capacity of the drum must be increased with the same rotative moment so that the energy consumption per weight unit will be smaller. In such a centrifuge the circumferential wall of the drum has rows of holes which are formed only in the regions of the top and bottom walls in order to make possible effective throttling of a low viscous sirup molasses up to an intermediate number of revolutions. In such a centrifuge the drum can be lengthened without the danger that the liquid fraction or sirup will be prematurely centrifuged.
Bending moments of the top and bottom walls of the drum cause tangential stresses in the circumferential wall in the regions of the top and bottom walls. The superimposed bending moments in the regions of the drum corners result in considerably high relative stresses which are similar to those in the central region of the circumferential wall. For these reasons it has been proposed to reinforce the circumferential wall of the drum in the regions of the top and bottom walls (German Auslegeschrift No. 1208694, German Offenlegungsschriften Nos. 1482740 and 1532698). The circumferential walls of such drums must be manufactured from a solid material by a turning-off process. Such a method of manufacture not only involves high material consumption, but also requires considerable working expenditures. For instance, a drum for accommodating 1000 kg of massecuite has the circumferential wall whose thickness in the central region is equal to 12mm and in the end regions is equal to 15-18 mm. Such a drum must be manufactured from a sheet material whose thickness is equal to 20 mm.
It has also been proposed (German Pat. No. 815,174) to provide the drum with a plurality of rings which are distributed over the entire circumferential wall and spaced from one another by small distances. In such a construction neither material economy, nor compensation for the stresses of the circumferential wall in the region of the top and bottom walls is attained.
Since a centrifuge is also utilized for centrifuging highly viscous molasses which cannot discharge through the holes located adjacent to the bottom wall during short braking periods of the process, it has been proposed to provide additional holes in the central region of the circumferential wall or to provide holes distributed over the entire circumferential wall (German Pat. No. 1,916,280). Since this requires reinforcing the drum in the central region, it has simultaneously been proposed to form such additional holes of an elliptic shape. However, the elliptic holes are labor consuming and expensive to manufacture.